1. Field of the Invention
The invention relates to a device for introducing digital signals into a medium having at least bivalent states comprising a data input for serially receiving a flow of data bits under the control of a first clock pulse series, and a coding device having an input which is connected to the data input and an output which is connected to said medium in order to apply thereto, under the control of a second clock pulse series, a flow of code bits which has been changed with respect to the flow of data bits by a commutation device while satisfying predetermined code restrictions, the code conversion having an efficiency 1/p which is smaller than 1, and wherein 1/p is a rational fraction. The medium may be a magnetizable tape which can be driven along a read/write head device. "Introducing" is to be understood to mean storing in this context. Alternatively, a channel for data transmission may be concerned. Introducing is then to be understood to mean transmitting. The data bits as well as the code bits may be bivalent or multi-valent, independent of each other. The code bits of a given value may imply a status transition (NRZ-1 code) in the medium. Other codes are also known, for example, the NRZ code. It is often desirable to add synchronization information to the code bits for auto-synchronization. Therefore, preferably a large number of status transitions occurs.
2. Description of the Prior Art
Notably known is an algorithm for limiting the number of directly successive code bits without transition, both within a single code word and in a succession of two or more code words. For example, P. A. Franasek, "Sequence-state-methods for run-length limited coding", IBM Journal of Research and Development, July 1970, pages 376-382, describes a variety of such codes. A known and frequently used method is that in which a data word comprising four data bits is converted into a code word comprising five code bits. Another known method having this property is the so-called Miller code which will be described in detail hereinafter. Also known are other mechanisms whereby data bits are converted into code bits while satisfying given code restrictions. The code efficiency of the coding device is almost always smaller than 1; in the above cases it amounts to 0.8 and 0.5, respectively. A problem exists in that some data generators exhibit an extremely high serial bit rate. An example of this problem is found in, television cameras, even those having a simple construction. Said medium may be provided with a single channel having a high bit rate, but sometimes this is very problematic, notably if use would have to be made of a linear recorder. This storage medium would then require a particularly large bandwidth. Similar problems occur in the case of a channel for data transmission. The invention has for its object to enable, in the described surroundings (but not restricted thereto), the use of channels in the medium which are capable of receiving only a limited bit rate, without each separate channel requiring its own coding device.